1. Field of the Invention
The present invention relates to a control method and apparatus for improving the speed change characteristics of a vehicle fitted with an automatic transmission.
2. Description of the Related Art
Heretofore, at the time of speed change of a vehicle automatic transmission, the engine torque is reduced by for example, reducing or stopping the fuel supply, retarding the ignition timing, reducing the intake air flow quantity by automatic opening control of the throttle valve (increasing the intake air resistance), or a combination of these, to thereby suppress the rapid change in torque of the transmission output shaft at the time of speed change, and hence alleviate speed change shock. The period for carrying out this torque down control should be the period where the speed change operation is actually being carried out, after the torque speed change has been transmitted (after lapse of the torque phase) after commencement of the primary speed change operation. Here, due to the start and stop operation of the speed change elements due to the speed change, the time when the speed change operation is being carried out can be considered as the period from when the speed change ratio between the output shaft of the automatic transmission and the turbine shaft (ie. the input shaft) of the torque converter starts to change from the gear ratio prior to speed change until this drops to the new gear ratio after completion of the speed change. This speed change operation period is referred to as the inertial phase (gear change period).
As conventional technology related to the above torque down control, there is the arrangement disclosed in Japanese Unexamined Patent Publication No. 5-321707.
With this arrangement, the throttle valve opening can be controlled automatically irrespective of the intention of the driver (for example the accelerator opening). As shown by the full line in FIG. 8, during the torque phase the throttle valve opening is increased by a predetermined amount, while during the inertial phase the throttle valve opening is decreased by a predetermined amount, thereby reducing the speed change shock. However, the torque phase and the inertial phase are detected by elapsed time from the time of a speed change requirement.
Moreover, with the arrangement as disclosed in Japanese Unexamined Patent Publication No. 6-129273, the throttle valve opening can be controlled automatically irrespective of the intention of the driver (for example the accelerator opening). As shown by the full line in FIG. 9, during the inertial phase the throttle valve opening is decremented to thereby effect a reduction in speed change shock. However the inertial phase is detected based on the speed change ratio between the output shaft of the automatic transmission and the turbine shaft (ie. the input shaft) of the torque converter.
With the abovementioned arrangements disclosed in Japanese Unexamined Patent Publication Nos. 5-321707 and 6-129273, there are the following concerns.
In general, the shorter the speed change time and the smaller the torque difference at the time of speed change completion the less the speed change shock, resulting in good speed change characteristics, but to achieve this, the torque down amount during the inertial phase must be made quite large. However if the torque down amount is made large, then when the throttle valve opening returns to the target opening for normal operation after completion of the inertial phase, since there is also a limit to the responsiveness of the throttle valve operation, then the return time is increased with the increase in the torque down amount. Hence a torque pull (a drop) occurs after completion of the inertial phase, so that speed change shock is increased. The driver is therefore likely to experience a different sensation (refer to the chain lines in FIG. 8 and FIG. 9).
With the above problem, even in the case where the torque down control is carried out by other methods (control of fuel supply quantity or ignition timing and the like), due to the response delay, the problem similarly arises.